The effect of foamed cement nanocomposite as counter electrode on the performance of dye-sensitized solar cell

Improper interparticle connection between carbon-based materials, poor interface bonding between the carbon counter electrodes (CEs) and substrate, and low surface area are the main limitations of carbon-based CEs in dye-sensitized solar cells. In this study, we utilized foamed cement and binder for adherence and surface area improvement in carbon-based CEs, such as graphite, multi-walled carbon nanotubes, and carbon black (CB). The results revealed that incorporating foamed cement into carbon materials improved the resistance, short-circuit current density, fill factor, and power conversion efficiency of the device. The porous cement/CB nanocomposite CE with a photoconversion efficiency of 5.51% exhibited the best photovoltaic performance. Moreover, this nanocomposite electrode showed an enhancement catalytic activity by high current density in cyclic voltammogram, low charge transfer resistance $(R_{CT}$) in electrochemical impedance spectroscopy, and high exchange current density in Tafel measurements compared to other electrodes. The porosity of foamed cement has been found to be the main cause of its superior photovoltaic performance, which expands the contact area with the electrode and enables rich ion transport. Additionally, the enhanced performance was due to strong bonding, crack-free deposited films, superior conductivity, and high catalytic activity.     

Mathematical modeling of crossflow microfiltration of diluted malt extract suspension by tubular ceramic membranes

The practical application of microfiltration in brewing industry is hindered by severe membrane fouling and subsequent permeate flux decline. A theoretical and experimental study on the effect of operating parameters, which influence the crossflow microfiltration of beer and beer quality was performed. A mathematical model is developed to better understanding of the fouling layer characteristics. The experiments were conducted for different ranges of pressures, temperatures and shear rates. An optimum transmembrane pressure of 1.1 bar is suggested to maximize both the steady state and average permeate fluxes. The results of numerical simulation were in a good accordance with the experimental data.     

Commutation modelling and sparks reduction based on coupled circuit method

The commutating machines have a notable effect on the exchanges in brush–commutator contact area, which is particularly obvious when determining the intensity of sparks located on the brush. With time, higher current density at the descending edge promote sparks excitation, which itself increases intensity of the electrical erosion, brush temperature and thus also the wear. So in order to make an analytical study of commutation phenomenon, the coupled circuit method was developed. Therefore, a generalized mathematical model of the commutation, for brush–commutator, is established and can be extended for any other types of commutation on the basis of electromagnetic field (e.g. transformers and phase shift transformer. This model provides a greater efficiency to explain the impact of the electromagnetic fluxes surrounding brush area (or switch), specially for the current transition of the commutation process. Successful commutation is defined as operation in normal service, with no serious damages to the commutator, brushes or switches due to sparking that might require abnormal maintenance. It is recognized that some visible sparking are not evidence of unsuccessful commutation. The recommendation to improve the commutation (to achieve longer brush life) is the implementation of the proposal (slotted brush), which provides a linear and a sweet transition of currents in the coils of commutation. Copyright © 2012 John Wiley & Sons, Ltd.     

MXene Free Standing Films: Unlocking the Impact of Flake Sizes in Microwave Resonant Structures in Humid Environments

Microwave communication devices necessitate elements with high electrical conductivity, a property which was traditionally found in metals (e.g., copper). However, in applications such as satellite communications, metals prevent the payload from achieving lightweight and flexible characteristics. Here, we demonstrate the development of MXene film microwave resonators, leveraging MXene's high electrical conductivity and unique mechanical properties. To investigate resonant performance in humid conditions and study the effects of MXene's processing and treatment, MXene films with different flake sizes are prepared and exposed to cyclic humidity. For the large- and small-flake Ti₃C₂ MXene films in cyclic humidity, the large-flake film demonstrates higher electrical conductivity, higher resonance quality factor (150 and 35 as unloaded, and loaded), and less fluctuation of performance (≈1.7% total shift in resonance frequency). Further, by implementing MXene films of two different diameters, the correlation between film size and resonant frequency is demonstrated. By introducing an active resonant configuration, the effect of MXene degradation and microwave losses can be compensated. This active feedback loop demonstrates a ≈300 times increase in the quality factor of MXene resonators. As a building block for terrestrial and satellite communication modules, MXene resonators potentiate the replacement of metals in achieving unique electrical and mechanical properties.     

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Hollow structural section (HSS) and concrete-filled tube (CFT) cross-sections have been widely employed in the columns and braces of special concentrically braced frames (SCBFs). Square-HSS cross-section widely used in multistory frames is filled with concrete and converted to square-CFT cross-section to enhance the behavior of this cross-section. However, some investigations indicated that circular-HSS cross-section filled with concrete (circular-CFT) showed better behavior in comparison with square-CFT cross-section due to more uniform and larger concrete confinement in circular-CFT cross-section. The current study was experimentally undertaken to evaluate (1) the seismic performance and the global and local hysteresis responses of HSS and CFT members with various cross-section shapes from initial elastic range to collapse in the system level of multistory SCBFs, (2) the behavioral differences between square cross-section and circular cross-section, and (3) the behavioral differences between HSS cross-sections and CFT cross-sections employed in the columns and braces of SCBFs. Four full-scale one-bay, two-story SCBFs with four various cross-sections, namely, square-HSS, circular-HSS, square-CFT, and circular-CFT, for columns and braces were subjected to cyclic lateral loading. Evaluating base shear–roof drift hysteretic loops of SCBF specimens demonstrated that SCBF specimens with CFT columns and braces (CFT-SCBFs) experienced respectively around 107%, 58%, 28%, and 152% higher stiffness, post-yielding and post-buckling strengths, ductility, and energy dissipation capacity than SCBF specimens with HSS columns and braces (HSS-SCBF). In addition, the experimental observations indicated that CFT braces experienced local buckling initiation, crack initiation, and fracture at respectively 2.22, 2.35, and 2.32 times of roof drifts of those exhibited by HSS braces. Moreover, assessing braces with various cross-sections indicated that CFT braces showed an increase in compression strength, post-buckling strength, compression axial deformation, and out-of-plane buckling approximately by 83%, 152%, 127%, and 100%, respectively, in comparison with HSS braces. Finally, square-HSS/CFT braces sustained rupture propagation better than circular-HSS/CFT braces.